Theoretical Study On The Electronic Structure And Magnetic Properties Of MnAl Alloy Based Surfaces And Heterojunctions

The degree of informatization is one of the indicators to measure the level of social modernization.Information technology is naturally being developed by countries,because it is also a key technology to enhance overall national strength.The big data service generated by information technology provides convenience for people's production and life,and also poses new challenges to information access technology.Seeking new storage media with higher storage density and faster storage speed has become a key research area in the development of information storage technology.The development of spintronics theory and the discovery of Heusler alloys have made it possible to develop new types of storage media.At present,magnetic storage media based on magnetic tunnel junctions are expected to break through the bottleneck of information storage density and speed.MnAl Hesuler alloy is semi-metallic and completely compensated ferromagnetism,and it is considered to be one of the best candidate electrode materials for synthesizing low-energy and high-sensitivity magnetic tunnel junctions.However,influences of the surface and interface effects on the electrical and magnetic properties of binary MnAl alloys is not known.For the diversity of binary MnAl alloy geometry,we considered three different crystal structures of D0₃,D0₂₂ and L1₀.We constructed corresponding bulk models and surface models of D0₃-Mn₃Al,D0₂₂-Mn₃Al and L1₀-MnAl alloys,and D0₂₂-Mn₃Al/GaAs heterointerface and L1₀-MnAl/GaAs heterointerface models.Through the first-principles method,the geometrical properties,magnetic anisotropy energy,electronic structure and thermodynamic stability of the binary MnAl alloy block model,surface model and interface model are studied.PBE,PBESOL,HSE and LDA+U calculation methods are used to calculate the formation energy of D0₃-Mn₃Al alloy and D0₂₂-Mn₃Al alloy.The results show that the crystal structure of D0₂₂-Mn₃Al is more stable.The calculation results of the surface model of binary MnAl alloy indicate that the surface of D0₃-Mn₃Al alloy is most likely to form an end face containing MnAl atoms.The surface of D0₂₂-Mn₃Al alloy is most likely to have an end face containing MnAl atoms.The surface of Al atom of L1₀-MnAl alloy is most likely to exist.The electronic structure calculation results of the three stable surfaces show that the surface of D0₃-MnAl has an electron spin polarizability of up to 84.16%,which is the surface with the highest degree of spin polarization in the three.Their magnetic anisotropy energy calculation results show that the easy magnetization axis of D0₃-MnAl surface is parallel to the surface,while the easy magnetization axis of D0₂₂-MnAl surface and L1₀-AlAl surface is perpendicular to the surface,and D0₂₂-MnAl surface has the largest perpendicular magnetic anisotropy energy.In the heterogeneous interface model of binary MnAl alloy,among the many interfacial structures composed of D0₂₂-Mn₃Al alloy and GaAs crystal,the bridge interface formed by the MnMn end face of D0₂₂-Mn₃Al alloy and the AsAs end face of GaAs crystal is the most stable,namely D0₂₂-AA-MM-B;In many interface structures composed of L1₀-MnAl alloy and GaAs crystal,the bridge interface structure formed by the AlAl end face of L1₀-MnAl alloy and the AsAs end face of GaAs crystal is the most stable,namely L1₀-AA-AA-B.In addition,the spin polarization of the D0₂₂-AA-MM-B and L1₀-AA-AA-B interface models are greatly improved compared to its corresponding surface models.Finally,the calculation results of the magnetic anisotropy energy of these two interface models show that they have large perpendicular magnetic anisotropy energy.The research work in this paper runs through the block,surface and interface of binary MnAl alloys,forming a relatively complete research framework.Our research work demonstrates the changes in electronic structure and magnetic properties of MnAl alloys from bulk to surface to interface.And the physical mechanism of surface effect and interface effect on the electronic structure and magnetic properties of MnAl alloy is revealed.Although the surface and interface structure of MnAl alloy exhibit excellent perpendicular magnetic anisotropy,the surface and interface effects of the MnAl alloy generally inhibit the electron spin polarization of MnAl alloy.Therefore,in order to overcome the adverse effects of surface and interface effects,further improvement measures are needed.In summary,the results of this paper have guiding significance for the experimental study of magnetic tunnel junctions made of MnAl alloy.